Corrosion inhibitors



United States Patent 3,281,279 CORROSION INHIBITORS Hugh F. Schaefer,Lakewood, Ohio, assignor to Union Carbide Corporation, a corporation ofNew York No Drawing. Filed Oct. 28, 1963, Ser. No. 319,566 7 Claims.(Cl. 136107) This invention relates to the inhibition of corrosion ofzinc and it more particularly refers to the inhibition of corrosion ofzinc in alkaline environment and to the prevention of the formation ofexcessive amounts of gas in an alkaline galvanic cell.

Zinc has been the most common anode material for galvanic cells for manyyears. In the past few years galvanic cells which utilize "an alkalineelectrolyte have gained prominence for many applications. It has beenfound that there is a certain amount of corrosion of the zinc anode inthese cells which is not productive of useful electric power. Very oftenthis corrosion occurs when the cell is in storage, and this, of course,tends to reduce the effective life of the cell when it is finally put inservice.

A solution has been proposed for this problem which is based upon thesaturation or near saturation of the electrolyte with products of zinccorrosion thus putting the system in equilibrium with respect to zinccorrosion. This has been accomplished by adding zinc oxide or zincateions to the electrolyte. It has also been found that the amalgamation ofthe Zinc anode very often aids in the inhibition of non-productivecorrosion by electrolyte. These proposals have worked well; however, itis desirable to have alternate materials which are effective bythemselves to inhibit zinc corrosion.

It is a primary object of this invention to provide materials whichinhibit the corrosion of zinc in alkaline environment.

It is another primary object to prevent the formation of large volumesof gas within a zinc cell and thus preserve the str-uctural integrity ofthe cell.

It is a more particular object to inhibit the non-productive corrosionof zinc anodes in alkaline galvanic cells.

It is another object to improve the characteristics of alkaline galvaniccells having zinc anodes.

This invention is based upon the discovery that there are certainorganic compounds which prevent the corrosion of zinc in alkalineenvironment without relying on the establishment of equilibriumconditions between zinc, alkali, and zinc corrosion products.

In accordance with this invention and the above stated objects, theinhibition of the corrosion of zinc is accomplished by the presence ofan inhibiting amount of benzyl tertb-utanol. This compound ischaracterized by the fact that it is: substantially passive to theelectrochemical reaction between zinc and an alkaline environment,chemically inert to both zinc and the alkaline environment andresistance to oxidation.

It has been found that this compound inhibits the corrosion of zinc inboth the solid form and in the powdered form. This inhibitor does notinterefere with the normal operation of the zinc as an electrode and yetis effective to inhibit non-productive corrosion of the zinc, and toreduce gassing associated therewith.

The term corrosion, refers to non-productive corrosion of the zinc anodewhich does not produce a usable galvanic current, unless otherwiseindicated.

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The above described corrosion inhibitor is effective when used with bothamalgamated zinc and non-amalgamated zinc. The corrosion of amalgamatedzinc, which is normally less subject to corrosion than non-amalgamatedzinc, is inhibited to a greater degree by the presence of the hereindescribed inhibitor. The corrosion inhibiting character of benzyltert-butanol has been found to be substantially stable and does notdiminish appreciably with the passage of time under normal storage andoperating conditions.

The inhibitor compound can be incorporated in the cell in several ways.For example, the selected inhibitor can be added directly to theelectrolyte prior to gelling the electrolyte. Alternatively, theinhibitor can be added directly to the anode material. For example, theinhibitor can be dissolved in a suitable solvent, e.g., acetone, and thepowdered zinc anode material then soaked in the solution. The solvent isthen evaporated and the treated zinc incorporated in the cell. Asanother method the inhibitor solution can be sprayed into the anodematerial. For use in galvanic cells it is preferred to add the corrosioninhibitor to the anode material. In any event a homogeneous distributionof the inhibitor is desirable to provide uniform protection.

The compound described is employed in an inhibiting amount, that is, anamount which is sufiicient to inhibit or substantially prevent theoccurrence of non-productive corrosion and formation gas. In general,amounts of about 0.01 to about 1.0 weight percent based on the weight ofanode material to be protected, i.e., on the weight of zinc, providesatisfactory corrosion inhibition. The actual amount of inhibitornecessary to provide adequate inhibition in any particular situation caneasily be determined by methods well known in the art.

To illustrate the advantageous characteristics of benzyl tert-butanolstandard D-size alkaline-manganese dioxide cells were prepared. Powderedzinc, which was amalgamated to the extent of about 4 percent by weightwas immersed for about 24 hours in a solution containing one percentbenzyl tert-butanol based on the weight of amalgamated Zinc. The solventwas then thoroughly evaporated in a vacuum oven at between 40 C. and 60C. The treated zinc was then incorporated in standard alkaline-manganesedioxide cells employing potassium hydroxide as the electrolyte.

Table I shows the voltage characteristics of cells containing thetreated anodes. Both open circuit potentials and those on a one-ampereload (by the interrupter technique) were observed. Substantially noeffect on cell performance was noted.

These cells were then discharged at 0.5 to 1.0 ampere continuous drainto approximately 50 percent of their capacity. Open and closed circuitvoltages of the used cells were then recorded. The range of voltages ofthe treated cells were approximately the same as the ranges observed incontrol cells, thus again indicating little or no effect of theadditives on cell performance. This particular test is believed to be avery severe one in that about percent of control cells, so discharged,showed excessive gassing and, in many cases, actual rupture of the cellcontainers occurred. After 50 percent discharge,

a series of treated and control cells were connected to mercurymanometers to measure gas pressure buildup over a period of 1 to 6months at ambient room tem- 1.0 weight percent based on the weight ofthe zinc anode. 7. The galvanic cell described in claim 6 wherein saidelectrolyte is an aqueous solution of potassium hydroxide and saidcathode depolarizer is manganese dioxide.

TAB LE I Voltage of Fresh Cells Voltage of 50 percent Discharged CellsAdditive Gassing of 50% Discharged Cells Open Circuit Closed CircuitOpen Circuit Closed Circuit (1.0 amp.) (1.0 amp.)

None 1.481.53 1.371.46 1. 241. 28 0.94-1.12 Excessive in majority ofcells: cell rupture observed in several cases even after 1 month andparticularly after 6 months at ambient room temperature.

Benzyl tert-butanol 1.50 1. 40-1. 43 1. 28-1. 29 1.07-1.15 Substantialreduction of gassing even after six months at ambient room temperature.

What is claimed is:

1. A method of inhibiting corrosion of zinc exposed to an alkalineenvironment which comprises effecting said exposure in the presence of acorrosion inhibitor comprising benzyl tert-butanol.

2. The method of claim 1 wherein said alkaline environment comprises .01to 1.0 weight percent, based on the weight of said zinc, of said benzyltert-butanol.

3. The method of claim 1 wherein said alkaline environment is an aqueoussolution of potassium hydroxide.

4. The method of claim 1 wherein said Zinc is amalgamated.

5. A galvanic cell comprising a zinc anode, a cathode depolarizer, analkaline electrolyte and benzyl tert-butanol in an inhibiting amount.

6. The galvanic cell described in claim 5 wherein the corrosioninhibiting amount is from about 0.01 to about References Cited by theExaminer UNITED STATES PATENTS 2,829,114 4/1958 Hervert 252387 X2,897,250 7/1959 Klopp 136l07 2,900,434 8/1959 Zimmerman et al. 136l07 X3,095,331 6/1963 Davis l36l07

1. A METHOD OF INHIBITING CORROSION OF ZINC EXPOSED TO AN ALKALINEENVIRONMENT WHICH COMPRISES EFFECTING SAID EXPOSURE IN THE PRESENCE OF ACORROSION INHIBITOR COMPRISING BENZYL TERT-BUTANOL.